Heat control device



Aug. 21, 1945.` l.. w. COOK 2,383,291

HEAT CONTROL DEVICE Filed Aug. 28, 1942 PaemedAua 21, 1945 Leonard Wt Cook, Stratford, Conn.,v ass'ignor to Company, a corporation of New General Electric York application somt-.2a. 1942,. sex-h1 No. 450,509

s claim. (ci. zoo-1:2)

My invention relates to heat control devices and more particularly to devices for .controlling electrically heated blankets and the like, and its object is to provide an improved control device of' that character which, is simple in construction,..

cheap to manufacture, and reliable in operation.

My invention will be better understood from the of suitable insulating material, such as plastic. is attached to the portion of the shaft I1 which protrudes from the front of the housing 8 in any suitable manner so that the shaft I 1 may be readily rotated to cause it to be moved, in or out relan tive to the front of the housing 8. The portion of following description whenX taken in connection,

with the accompanying drawing, and its scope will be pointed out inthe appended claims.

In the accompanying drawing, Fig. 1 is a front elevation view of one form of my improved heat control device; Fig. 2 is a sectional view of the device taken along line 2-2 of Fig.l l and looking in thedirection indicated by the arrows; Fig. 3 is a back view of the device with the back cover removed;f Fig. 4 vis Aa. sectional view of the device taken along the line 4-.4 of Fig. 3iand looking in same view as Fig. 4 except the line switch is shown in its closed position; and Fig. 6 diagrammatically illustrates a blanket control system embodying my new control device; j

Referringl to the drawing, my control device 1 comprises a housing or basel of suitable insulating material, such for example as plastic or other molded material. This housing 8 is so formed lthe direction indicated by the arrows; Fig. 5 is the the shaft I1 which protrudes from the bushing I3 toward the interior of he device 1 is knurled'and also has a portion of its round surface flattened. This portion of the shaft is surrounded by a collar I8 having two projections 20 and 2i spaced slightly less than 180 degrees apart. These projections 20 and 2i are arranged to engage a projection 22 extending toward the :interior of the housing 8 so as to limit the rotation of the shaft I3 to substantially one-half of a revolution. In threaded engagement with the inner portion of the shaft I1.`

is a threaded screw 23 having a round head which projects toward the interior of the housing 8 from the inner end, of the shaft. With` the construction so far described, it will be observed that rotation of the knob I8 in one direction causes the rounded head of the screw 23 to move'toward the that it constitutes the front and sides of my im proved control device. l'I'he back of the housing 8 is arranged to be covered byA a cover Ithat is fastened to the housing B by screws I0. An escutcheon plate I i of suitable material, Isuch as sheet brass, covers a portion of the front and botytom of the housing 3, this escutcheon plate being held in place by an'extension I2 at the bottom thereof which extends upwardly along a portion of the back of the housing 8 below the cover 9 and by means of a metallic bushing I3 which extends through an opening in the front of the housing 8 and the escutcheon II. One end I4 of the bush.-

ing I3 is enlarged and polygonaliy shaped and is' inserted in a similar shaped Opening in the inner surface of the housing so as to prevent rotation of vthe bushing. 'I'he other end Il of the bushing lthreaded surface of the bushing I3. 'A knob I3 back of the housing 8 and rotation of the knob I8 in the opposite direction causes the rounded end of the vscrew 23 to move toward the front of the housing 8.

The rounded end of the screw 23 engages a rectangular-shaped plate 2l of insulating material. one end of which, together with one end of a similar shaped brass plate 25 and one end-of a b1: metallic member 28 are riveted to a spring or flexible support 21, whichin turn is-secured to the inner side of the housing 8 by screws 28. The free end of the bimetallic member 26 carries a contact 23 which' is arranged to engage a stationary contact 33 mounted near the end of one of the arms of an L-shaped member 3| of flat conduct-v ing material, such. as brass, which is fastened to the 'housing 8 by a screw 32. Movement of the screw 23 as a result of rotating the knob I8.there forel -ilexes the spring support 21 so as to vary the position of the bimetallic member 2 3 and contact 23 with respect'to the fixed contact 30. When the screw 23 is moved toward the back. of the erwise secured to the member3l and a flat contacting surface 34 of suitable non-magnetic material such as silver, soldered or otherwise secured across the two pole faces of the magnet 33. The movable contact 29 is made of suitable magnetic material, such as steel, on which is secured by any suitable means, such as rolling or welding, a sheet of suitable contacting material 23', such as silver, so that a silver-to-silver contact is obtained when the contacts 29 and 30 are in engagement.

In order to obtain the proper temperature differential of operation, the stationary contact 36 is secured to the member 3| which is moved relatively to the movable contact 29 so as to change the amount of flux threading the magnet 33 and the magnetic material in the movable contact 29 to the proper amount to produce the desired calibration. Then member 3| is securely anchored by screw 32 at the position thereon that produces the proper calibration.

In order to materially reduce the effect on the temperature of the bimetallio member 24 of any are established'between the contacts 29 and 36, such heating effect is localized at the free end of the member 24 by restricting the cross-section of the portion of the member 26. 'I'his result is obtained in the arrangement shown by providing the holes in the bimetallic member 26 just above the contact 21 so that the thermal resistance between the contact 29 and the main body of the member 26 is high.

A small electric heater 35 of any suitable type is fastened to the inner surface-of the portion of the housing 8 which constitutes the front of the heat control device 1 by suitable means, such as the screws 36. As shown, the heater 36 is arranged in the form of a coiled heater (not shown) encased within a hollow porcelain cylinder through which passes one of the leads 31 that supplies current to the heater 35. 'Ihis heater 35, which has a relatively high thermal time constant is so located between the bimetallic member 26 and the housing 6 that the heating of the bimetallic member 26 varies in accordance with the current flowing through the heater 35.

In the lower portion of the housing 6 is located a manually controlled switch for opening and closing the circuit through the heating device whose temperature the control device 1 is arranged to control. This switch comprises a flat spring contact member 38 which is arranged to be moved into and out of engagement with a stationary contact 39 secured tothe other arm of the L-shaped member 3| than the one to which the stationary contact 30 is secured. The spring contact member 38 comprises a spring blade, one end of which is secured to the inner surface of the housing 8 by a screw 40 and the other end of which has a contact 4| secured thereto. The spring member 38 is arranged to be flexed by means of a cam and operating trigger member 42 of suitable molded insulating material and provided with projecting cylindrical sections 43 which rotate in the housing 8. 'I'he trigger section of the member 42 consists of two sectors 44 and 45 which extend through an opening in the front of the housing 8 and which are so arranged that counterclockwise rotation of the trigger member causes the sector 44 to protrude from the front of the housing, whereas clockwise rotation of the trigger member causes the sector 45 to protrude from the front of the housing. One of these sectors, such as 44 for example, may be painted or otherwise marked in any suitable manner so that the condition semispherical surface 46, preferably of steel,

projecting from its surface at a point intermediste the two nat surfaces 46 and 41 and which moves into a hole 46 in the spring member 36 when it is in its open circuit position shown in Fig. 4.

'Ihe normal tension of the spring member 36 causes it to press forcibly against the member 42 at all times, and therefore it firmly maintains the trigger member 42 in each of its two positions. The member 42 is held within the housing 3 by an anchor plate 66 secured to the housing by the screws 5| which anchor plate bears against the cylindrical sections 43 of the trigger member 42 thereby confining them within the bearing sections of the housing. The anchor plate 66 also has an extension 52 containing an opening 53 through which the spring member 36 extends. The top edge of the opening 63 acts as a fixed fulcrum point for the spring member 36 so that when the center section of the spring memberis forced upward and away from the dat portion 46 of the cam member 42 by the semispherical member 46 moving out of the hole 46 and under the spring member 36 and by the positioning action of the surface 41 of cam 42 when the trigger member 42 is rotated clockwise from the position shown in Fig. 4, the free end of the spring member 36 is deflected'downwardly so that the contact 4| on the spring inember 36 engages the stationaryr contact 36, .as shown in Fig. 5. Similarly, when the trigger member 42 is rotated 1n a clockwise dirccucn from the position shown in Fig. 5 to the position shown in Fig. 4, the semispherical member 46 moves from under the spring member into the hole therein so `that the normal tension of the member 36 causes the center portion thereof to move downwardly and the free end thereof to move upwardly about the edge of the opening 63 as a fulcrum so that the contact 4| is moved out of engagement with 'the stationary contact 39.

The control device 1 is arranged to be connected in the electric circuit to be controlled thereby by establishing a connection to a terminal 54 which is secured to and in electric contact with the bimetallic member spring support 21 by one of the screws 28 and a connection to a terminal 55 which is secured to and in electrical contact with one terminal of the heater 35 by one of the screws 36. The electric connections of the various elements of the control device 1 will be more clearly seen from the diagram shown in Fig. 6 which illustrates a control system for an electric blanket embodying my control device. In this Fig. 6, 66 represents an 'electric blanket having a heating resistor 61, the

ends of which are connected to a pair of terminal pins 59 that are adapted to be engaged by a pair of contacts 69 provided in a supply plug 66. The contacts 59 are respectively connected to the secondary terminals of a step-down transformer 6|, the primaxywinding of which is connected 4to a supply plug 62 through the control device 1. From Fig. 6 it will be seen that when the trigger member 42 of the control device 1 is in the position shown in Fig. 5. the primary winding of the transformer 6| is connected in series with the bimetallicmember 26, contacts 29, 30, 39, and 4I, the spring member 38, and the heater I5. Therefore, when the trigger switch is in the position shown in Fig. 5, the electric energy input to the blanket B is` controlled by the proportion of time that the contacts I9 and 4| are in engagement to the time that these contacts are out of engagement. These times are controlled by the temperature of the bimetallic element v24, which is jointly dependent upon the room temperature and upon the heat supplied to the bimetallic element from the auxiliary heater 35. For a given unchanging room tem' perature, the bimetallic element 26 controls the time of engagement of the contacts 2s and I0 so as to maintain the temperature oi the blanket at a substantially constant value. When the room temperature varies, however, the amount of energy input into the blanket is varied since thus, if for a. given setting of the control device, the room temperature should decrease, the heat that would be imparted to the bimetallic elementA 24 from'the room is reduced and therefore it requires a, longer period of time for the auxiliary heater 35 to heat the bimetallic member 26 to the temperature at which it causes the contacts 29 and 30 to disengage than it did before, and after these contacts have opened and the auxiliary heater 35 is deenergized, the thermostatic element will cool quicker to cause the contacts to reengagedue to the increased cooling action of the room. These two actions of delaying the.

separation of the contacts and in advancing their closing result in an increase in the proportion of time that the contacts are in engagement over any given interval oi time. The control, therefore, supplies more energy to the blanket during a given time interval so as to maintain the temperature of the blanket at a predetermined value in spite of the decrease in rooml temperature. Conversely, when the room warms up, the pro portion of time that the contacts 29 and 30 are in engagement to the time that they are out of engagement is decreased so as to decrease the total amount of energy supplied to the blanket during a given time interval.

The transformer 8| functions to reduce the voltage of the supply line to a relatively low value so .as to eliminate any danger of shock by the user of the blanket.

While I have, in accordance with the patent statutes, shown and described my invention as applied to a particular construction and as embodying various devices, changes and modifications will be obviousto those skilled intheart, and I therefore aim in the appended claims to cover all such changes and modifications as fall within the true spiritand scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In combination, a housing of insulating material, a. bimetallic member having one end fastened to said housing and an electric contact mounted on the other end thereof, contact secured to 'said housing and adapted to be engaged by said first mentioned contact; said first mentioned contact being of a magnetic material having a contacting surface of suitable material and said stationary contact comprising a magnet having a contact of suitable non-magnetic material secured across the poles of said magnet and forming the contacting surface thereof engaged by said first mentioned contact.

2. In combination, a fixed support, a bimetallic member having one end fastened to said support and a contact mounted on the other end thereof, a stationary contact arranged to be engaged by said first mentioned contact to establish a series circuit through said member and said contacts, and means for localizing the heating effect on said bimetalllc member of any arc established between said contacts.

3. In combination, a fixed support, a stationary contact, and a movable contact mounted on one end of a bimetallic member, the other end of said member being fastened to said suppont, said member being of relatively small area aci-'- jacent to the point where said movable contact is mounted thereon in comparison to the main body of said member in order to establish high thermal resistance to Ithe transmission to the main body of said member of heat developed by an established arc between said contacts.

4. In combination, a housing of insulating material, a bimetallic member having one end thereof fastened to said housing and an electric contact secured to the other end thereof, a stationary contact secured to said housing and arranged to be engaged by said rst mentioned contact, a heater interposed between said bimetallic member and the inner surface of one side of said housing, and a metallic plate held in contact with the outer surface of said one side of said housing and functioning to radiate the heat supplied to said one side of said housing by said heater.

5. In combination, a housing of insulating material, a bimetallic member having one end thereof fastened to said housing and an electric contact secured to the other end thereof. a stationary conducting member secured to said houslng and having a contact secured thereto for engagement by said first mentioned contact, a fixed contact secured to said conducting member, a movable contact attached to said housing, and a cam rotatably mounted in said housing for moving said movable contact into and out of engagement with said ilxed contact.

LEONARD W. COOK.

a stationary i 

